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colour index
colour index The difference between the apparent magnitudes of a star at two different wavelengths, as measured through filters of different colours, e.g. B (blue) and V (yellow-green). B — V and U — B are typical colour indices. In Johnson photometry and Kron–Cousins RI photometry, all colour indices are made zero for a star of spectral classification A0V (e.g. Vega). Generally, hotter stars have negative colour indices, and cooler stars positive ones. Nowadays colour index is usually shortened to ‘colour’.
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"colour index." A Dictionary of Astronomy. 1997. Encyclopedia.com. 31 May. 2012 <http://www.encyclopedia.com>. "colour index." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 31, 2012). http://www.encyclopedia.com/doc/1O80-colourindex.html "colour index." A Dictionary of Astronomy. 1997. Retrieved May 31, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-colourindex.html |
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colour index
colour index The total volume percent of mafic (coloured) silicate minerals in an igneous rock. The mafic minerals would include the olivine group, pyroxene group, and amphibole group of minerals, as well as biotite. Colour index is one of many methods used for classifying igneous rocks. If a rock has 60% modal mafic minerals it has a colour index of 60. Rocks with colour indices between 50 and 90 are termed ‘mafic’ rocks (e.g. basalts).
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Cite this article
AILSA ALLABY and MICHAEL ALLABY. "colour index." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 31 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "colour index." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 31, 2012). http://www.encyclopedia.com/doc/1O13-colourindex.html AILSA ALLABY and MICHAEL ALLABY. "colour index." A Dictionary of Earth Sciences. 1999. Retrieved May 31, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-colourindex.html |
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